Wheelchairs have been primarily designed to provide transportation for the physically impaired, often emphasizing user comfort, portability and flexibility. Because of the individual needs and requirements of the wheelchair occupants, however, a variety of styles and shapes have been developed which cater to their specific needs. Moreover, most of these styles and shapes include power driven counterparts which, of course, are highly desirable.
Powered wheelchairs generally include an electric powered drive assembly having a drive assembly support structure which forms an integral portion of a wheelchair support frame. Typically, the drive assembly includes an electric motor and battery, each of which are generally mounted to the drive assembly support structure. At least two power driven wheels, supported by the wheelchair support frame, are rotatably coupled to the motor and engage the ground to propel the wheelchair. Furthermore, the wheelchair support frame carries a seat support assembly including a seat and a backrest. The drive assembly is usually operably coupled to a joystick which permits the user to control the direction of travel of the powered wheelchair from the user operational position.
While powered wheelchairs are highly advantageous in many situations, manually propelled or operated wheelchairs also can have many advantages. Moreover, if the drive assembly of a powered wheelchair should malfunction, for whatever cause, the wheelchair occupant may be left without a functional wheelchair for the duration of the repair period. Usually, the motor and/or batteries are individually mounted to the drive assembly support structure which, in turn, is integrally mounted to the wheelchair support frame. Repair of the damaged components often requires complete removal from the drive assembly support structure, and hence, the wheelchair support frame which involves a complex task reserved for the skilled technician. Moreover, removal of the complete drive assembly may require a piecemeal removal of each drive component. That is, the drive assembly cannot be readily removed from the wheelchair support frame as an independent unit. Thus, the whole wheelchair apparatus must be brought in for repair. During this repair time, the wheelchair user may be without recourse.
Typical of such prior art powered wheelchair assemblies are the wheelchairs disclosed in U.S. Pat. No. 5,022,476 to Weege; U.S. Pat. No. 4,961,473 to Jones; U.S. Pat. No. 4,805,712 to Singleton; and U.S. Pat. No. 4,341,278 to Meyer, each of which describes an electric powered wheelchair having a drive assembly support structure forming an integral part of the wheelchair support frame.
Attempts have been made to modularize the drive assembly to aid removal of the components. U.S. Pat. No. 4,967,864 to Boyer et al. discloses a powered wheelchair apparatus having modularized individual components formed for easier removal from the drive assembly. While the Boyer wheelchair may facilitate removal of the individual components, the drive assembly, as a unit, is not removable.
Still other attempts have been made to retrofit independent electric drive units to manually operable wheelchairs. U.S. Pat. No. 4,967,865 and U.S. Pat. No. 4,386,674 to Coker disclose detachable electric drive units mountable proximate a front portion of the wheelchair. This device however, poses several problems. The forward mounting of the drive unit severely hampers the user's entry and exit of the wheelchair when the drive unit is installed, as well as impedes the movement of the user once situated in the operating position. This problem can be magnified for those users severely impaired. Additionally, the pivotal motion of the steering precludes the effective use of footrests for the occupant.
Moreover, powered wheelchairs are often bulkier and substantially heavier than their manually operated counterparts. The weight of the motor, in addition to the battery, can be significant. A battery alone may weigh in excess of 20 lbs. Moreover, two batteries are necessary in most instances. The wheelchair support frame must also be designed to accommodate this additional weight which itself adds weight. Thus, wheelchair users often prefer manually operable wheelchairs for home use. The additional bulkiness of powered wheelchairs impairs maneuverability inside close quarters. Further, the power driven wheels together with the additional weight can wear or damage the floors and rugs of a home. Accordingly, it is highly advantageous for the user of a powered wheelchair to also own a manually operated wheelchair for home use. Unfortunately, this requires the wheelchair user to have two wheelchairs at his or her disposal, which is costly and requires storage space.
Additionally, if the wheelchair user has only a powered chair, when drive assembly malfunctions occur, the wheelchair must be pushed about manually. This task is cumbersome and requires assistance because of the additional weight of the powered chair and the lack of user operable drive wheels. Thus, dual usage of a powered wheelchair as both a powered and a manually operated chair has not been practical.
Another problem associated with powered wheelchairs is that they are not as portable as manual wheelchairs. Manually operated wheelchairs are much easier to transport in automobiles because they often do not require any special vehicle modifications or accommodations. The collapsibility of many manually operated wheelchairs makes them particularly suitable for portability in vehicles. In contrast, most powered wheelchairs, because of the integral mounting of the drive assembly onto the support frame, occupy substantially more space and are usually not a collapsible as their manually operated counterparts. Moreover, the additional weight a powered wheelchair carries substantially impedes the lifting of the wheelchair into vehicles. Often special vans or automobiles having modified exteriors and interiors are necessary to lift and transport powered wheelchairs.
Still other problems associated with powered wheelchairs are that they have a tendency to tip backwards upon initial acceleration. The torque generated by the motor is often substantial and the unwary user may tip over. In light of this problem, anti-tip caster wheels are often provided rearward of the drive wheels. These caster wheels often are mounted on arms rigidly coupled to the support frame and are angled downward to a level just above the ground. As the wheelchair begins to tip backward, the anti-tip caster wheels engage the ground to prevent further tipping. Typical of this type of structure is the wheelchair of U.S. Pat. No. 4,721,321 to Haury et al.
While these anti-tip mechanisms have successfully prevented rearward tipping of the wheelchair apparatus in most instances, the rigid coupling of the anti-tip wheel to the support frame provides a fairly abrupt jolt to the wheelchair occupant as the anti-tip wheel engages the ground. In one instance, the occupant's momentum is pivoting rearward about the drive wheel axis; in another instance the occupant's momentum is shifted forward as the anti-tip wheel engages the ground. This momentum shift may jolt the occupant which can be physically tolling, particularly on those severely impaired.
Accordingly, it is an object of the present invention to provide a wheelchair apparatus which is operable as both a powered and a manually movable wheelchair.
Another object of the present invention is to provide a wheelchair apparatus with a removably mounted drive assembly.
It is another object of the present invention to provide a powered wheelchair apparatus which is more portable.
Still another object of the present invention is to provide a powered wheelchair apparatus which lowers the composite center of gravity.
Yet another object of the present invention is to provide a progressively rated anti-tipping suspension to a wheelchair apparatus.
It is a further object of the present invention to provide a wheelchair apparatus which is durable, compact, easy to maintain, has a minimum number of components, is easy to use by unskilled personnel, and is economical to manufacture.
The apparatus and method of the present invention has other objects and features of advantage which will be more readily apparent from the following description of the Best Mode of Carrying Out the Invention and the appended claims, when taken in conjunction with the accompanying drawing.